A device of said type is known from U.S. Pat. No. 6,343,111 B1. Said known device includes a recording device having an x-ray source and an x-ray detector. Projection images of an object being examined can be recorded successively in a high-energy range and a low-energy range by means of said recording device. A combined image can then be produced by an evaluation unit from the projection images recorded in the high-energy and low-energy range.
Because the absorption behavior of the irradiated material of the object being examined differs depending on the energy of the irradiating beam, by combining the projection images it is possible to produce combined images reproducing the structural distribution of a specific material within the object being examined. For example structural distributions of two different materials having different absorption characteristics can be resolved when two projection images are recorded in different energy ranges.
The quality of the combined images will therein be all the better the further apart the high-energy range and low-energy range are. It is furthermore necessary to set the recording device's recording parameters in such a way that projection images exhibiting a sufficiently good signal-to-noise ratio will be produced in both the high-energy and low-energy range so that the image quality of the combined image will also be good. It must, though, be noted in this regard that in order to avoid motion artifacts the projection images must be recorded within a short interval one after the other in the high-energy and low-energy range. Moreover, the exposure to radiation of the object being examined must as a rule be kept as low as possible. The recording device's recording parameters must for this purpose be matched to the absorption characteristics of the object being examined.
Matching of said type does not, though, take place in the case of the known method.